GROUND RADIO bulletin no. 6 - june 6, 1949__________________________________________COMMS. DEPT. L.A.D.
4WFTA INT/EXT switch
Most of our4WFTA transmitters have a small bakelite panel, with two toggle switches and a rheostat, mounted in back of the RF chassis near the crystals. The panel is used to select internal or external keying voltage and to adjust this voltage to the proper value at the keying relay. We wish to have these panels installed on all ¿iWTFA transmitters so if there are any transmitters at your station which require them, they should be ordered by requisition. This addition to the transmitter was originated back in the old days before the modifications were numbered and consequently this is not a numbered modification. 4WTFA Int/Ext key voltage panels are available under PM #818&-7392.
NC240 OUTPUT TRANSFORMER
In most cases, we operate our NC-240 receivers without 6V6 output tubes. This results in no current flow through the speaker output transformer and, therefore, no heating of the transformer. The result has been an accumulation of moisture and corrosion within the speaker output transformer causing failure of the item. The failure naturally doesn*t show up until an attempt is made to use the speaker output terminals. This information is being passed along as an aid in locating common troubles.
ATU-RT TUNING UNIT
A recent report from POS has again called our attention to a characteristic of the ATU-RT. The spacing between the ends of the coils L and LB is small and results in a voltage breakdown on modulation peaks when an RFA-50, 12ACX-2A, GBAO combination is used. This gap has also been known to break down with an improperly tuned tower fed by a 12ACX-2A transmitter. In the case of high power, the natural remedy is to increase the gap spacing. This is done by removing one turn from the adjacent ends of the two coils. The tower tuning should then be rechecked.
